Technical Field
The disclosure relates to thermally deformable face seals and respirators including such face seals. More particularly, the disclosure pertains to thermally deformable face seal structures comprising composite phase change materials that mold to the face of a user to provide a personalized but one-size-fits-all facial fit.
Description of the Related Art
Respiratory protective devices are conventionally used in the workplace and by consumers to provide protection from respiratory inhalation hazards including particulates, gases and vapors. Typical respirator masks include a protective shell that covers the nose and mouth of the wearer with an incorporated filter that prevents contaminants in the air from being inhaled by the wearer. The effectiveness of respiratory protective devices to be used in a workplace in the U.S. is classified by the Occupational Safety and Health Administration (OSHA) by a value referred to as the assigned protection factor, or APF. The APF of a respiratory protective device is the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program. A primary factor that influences the APF rating of a respiratory protective device is the facial fit of the facepiece. In this regard, improper facial fit is a primary source of leakage for respiratory protective devices utilizing face seals, such as half facepieces, full facepieces, tight fitting powered air-purifying respirator (PAPR) facepieces and filtering facepiece respirators. No matter how efficient the respirator filter, if a facepiece does not fit properly then gaps between the mask and the face will allow particulate impurities to enter the breathing zone of the wearer.
Conventional respirators are most typically held in place by adjustable straps, elastic bands and nose clips that are adjusted to form a tight seal about the wearer's face. However, the tight fit often makes the respirator uncomfortable to wear and the respirator often will not maintain a consistent seal about the face during facial movement such as during speech or a change of facial expression. In addition, with the great variations in face shapes and sizes among potential users, attempts at designing a comfortable, one-size-fits-all respirator that can achieve a perfect face seal for all users have been generally ineffective.
For example, U.S. Pat. No. 4,454,881 teaches a filtering face piece respirator including a strap member and a mask body that incorporates a filtering material and an injection molded rubber edge bead element attached around a periphery of the mask. The strap holds the mask body against the face and the edge bead provides a seal between the mask and the user's face. An inwardly extending membrane component is also provided to improve the seal and reduce air leak around the nose and cheekbones of the wearer. However, the injection molded seal is weak and susceptible to detachment from the mask body after extensive use.
U.S. pre-grant publication 2012/0125341 teaches a filtering face-piece respirator having an overmolded face seal. The respirator includes a mask body and a harness, with the mask body including a support structure, a filtering structure and a face seal element. The face seal element is overmolded onto a portion of the perimeter of the support structure and is alleged to avoid the seal detachment risk of the seal taught in U.S. Pat. No. 4,454,881. However, their seal is formed from materials that are molded into a specifically defined shape that is not adaptable to the varied shapes and sizes of varied users, and are not suitable for a one-size-fits-all respirator. In this regard, analogous to the inwardly extending membrane portion of U.S. Pat. No. 4,454,881, the face seal of U.S. 2012/0125341 requires the addition of a very thin (less than 1 mm thick), inwardly extending flange portion to that can conform to the wearer's face to further provide for a snug fit. This flange must too be molded into a specific face-fitting configuration and is susceptible to fatigue induced degradation resulting from repeated flexing as the mask is repeatedly put on and taken off by the wearer.
Accordingly, there remains a need in the art for a respiratory protective device having an effective and comfortable face seal that can adapt to faces having nearly any shape and size, with improved shape retention after use and improved long term durability. The present disclosure provides a solution to that need.